The harm of nicotine in tobacco to human health is an indisputable fact. It is well known that tobacco specific nitrosamines (TSNAs) in tobacco can result in cancers. Of them, 4-(methylnitrosamine)-1-(3-pyridine)-1-acetone (NNK) in the TSNAs is one of the most harmful components inducing cancers. The notion of which smoking is harmful to health is well-established. Therefore, in view of human health, reducing the contents of nicotine and TSNAs in tobacco as much as possible has been of interest in the tobacco industry and other industries. Presently, there exist the following approaches to reduce nicotine and/or TSNAs in tobacco.
I. Nicotine inhaled into an organism is reduced by utilizing formulation technologies in production processes of tobacco products, thereby reducing the content of nicotine and or TSNAs. For example, as disclosed in Chinese Patent Publication No. CN1351852A, additives such as tea polyphenols, potassium citrate, potassium tartrate, and tannin are added into the formulation of tobacco to reduce the content of nicotine. As disclosed in Chinese Patent Publication No. CN1757337, additives prepared with porphyrin compound are added to the filters of cigarettes and/or tobacco blend of cigarettes, so as to reduce the content of TSNAs. Further, as disclosed in Chinese Patent Publication No. CN101015391, a composite additive containing a tobacco extract, an alkali metal salt and a metal hydroxide is added to tobacco leaves or tobacco blend, so as to reduce the content of TSNAs. In this approach, certain additives are expensive. Although some additives are of natural ingredients, the extraction procedures of active ingredients are troublesome and laborious. Additionally, some additives are of inorganic chemical ingredients, which may have risks in harmful residues.
II. Harvested tobacco leaves are treated with plant-derived agents or microbial preparations to directly reduce the nicotine content in tobacco. For example, as disclosed in Chinese Patent Publication No. CN101288504A, an ixeris denticulata extract is sprayed onto sun-baked tobacco leaves, and then naturally dried in shade, so as to reduce the nicotine content in tobacco. As disclosed in Chinese Patent Publication Nos. CN1579260 and CN1580237, microbial preparations containing strains KenLxP30 and KenLXR34 are applied respectively, so as to reduce the TSNAs content in tobacco. However, such an approach definitely increases the process steps and equipment for cigarette production. In addition, improper controls may cause the impairment to sensory quality of the tobacco.
III. Another approach is to reduce of the nicotine content in tobacco leaves when tobacco is planted and cultivated in the field.
1. Tea fertilizer is applied to the soil to reduce the nicotine content in tobacco. This approach has certain effects, but is very costly. There are limitations in a large-scale field cultivation of tobacco.
2. Microorganisms or microorganism metabolites are directly used to reduce nicotine in ripe tobacco leaves, so as to directly reduce the nicotine content in tobacco. For example, as disclosed in Chinese Patent Nos. ZL200410079650.6 and ZL200410079651.0, biological preparations prepared with Arthrobacter strains AS-1 and AS-2 are respectively used to reduce the nicotine content in tobacco. Although the cost of agent production is low, there are difficulties in the temperature and humidity controls in the tobacco curing process.
3. Growth hormones or other chemical agents are applied to the plant, so as to reduce the nicotine content in tobacco. For example, in “Regulating Effect of Nicotine Content of Flue-Cured Tobacco with Exogenous Regulators” (Feng, Ding, Thesis for Degree of Master, Nanjing Agricultural University, 2006), Feng Ding proposes to use 2,4-dichlorophenoxyacetic acid (2,4-D) or a combined agent of BF1 and choline chloride (CC) to reduce the nicotine content in tobacco. The nicotine reducing agent such as 2,4-D and CC has significant effects in nicotine reduction. However, applications of a chlorine element in a large amount not only are harmful to the ecological environment, but also cause chlorine remaining in tobacco, which is prohibited for tobacco.
Additionally, in “Effects of exogenous IAA on activity of ODC, MPO, MPT and nicotine content in flue-cured tobacco” (Acta Tabacaria Sinica, 2005, 11(6)), Huashan Liu et al report that certain effects are achieved by using indolylacetic acid to reduce the nicotine content. In “Effects of Nitrogen, Remained Leaves and α-NAA on the Nicotine of Flue-cured Tobacco Variety K326”, (Journal of Shanxi Agricultural University 2005, 25(3)), Wenxia Gao et al report that certain effects are also achieved by using naphthylacetic acid (α-NAA). However, in both chemical adjustment methods, a single ingredient is used, and the nicotine reducing level is limited. Further, the yield is not so stable. Thus, the two methods have little value of applications. Currently, no report regarding methods of applying exogenous salicylic acid and salicylic acid in combination with naphthylacetic acid or indolylacetic acid to reduce the nicotine content in tobacco is available domestically and internationally.
With respect to applications of salicylic acid in the field of plant cultivation, salicylic acid is an exogenous regulator for improving synthesis and metabolism of a target ingredient in the field of plant cultivation. Roles of salicylic acid as signaling molecule in plant disease resistant response and as stress resistant signaling molecule for inducing a plant to respond to abiotic stresses such as drought, low temperature, and saline damage are reported in many plant physiology researches. For example, application of 2 mmol/L salicylic acid can alleviate the damage of drought stress to bean seedling, application of 0.5 mmol/L salicylic acid can enhance the tolerance of corn to low temperature, and application of 0.1 g/L salicylic acid can improve the resistance of wheat to saline damage (Xin Sun, Yunmei Guo et al., Effects of Salicylic Acid on Several Physiological Indexes of Kidney Bean under Water Stress [J]. Journal of Sichuan University, 2005, 42(3); and Yifan Zhang, Mi'na Zhu, Discussion on Physiological Effect of Salicylic Acid in Plants [J]. China New Technologies and Products, 2009(1)). In addition, Chinese Patent Publication No. CN1476756 discloses the use of salicylic acid in growth regulation, which uses a composition containing salicylic acid or a salt thereof, amino acids and vitamins to improve potassium content and disease resistance of tobacco. Furthermore, in U.S. Pat. No. 7,691,630, a preparation containing salicylic acid is applied to improve the disease resistance of plants, so as to improve the yield and quality of crops. However, so far, in the field planting and cultivation of tobacco there have been no patents or literatures regarding application of aqueous salicylic acid solution or a mixed solution of salicylic acid and naphthylacetic acid or indolylacetic acid in water to reduce nicotine and (or) TSNAs in tobacco leaves.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies